Unravelling the Mechanism of Intermediate‐Temperature CO<sub>2</sub> Interaction with Molten‐NaNO<sub>3</sub>‐Salt‐Promoted MgO
Wanlin Gao, Jiewen Xiao, Qiang Wang, Shiyan Li, Michalis A. Vasiliades, Liang Huang, Yanshan Gao, Qian Jiang, Yiming Niu, Bingsen Zhang, Yuefeng Liu, Hong He, Angelos M. Efstathiou
Abstract
Abstract The optimization of MgO‐based adsorbents as advanced CO 2 ‐capture materials is predominantly focused on their molten‐salt modification, for which theoretical and experimental contributions provide great insights for their high CO 2 ‐capture performance. The underlying mechanism of the promotion effect of the molten salt on CO 2 capture, however, is a topic of controversy. Herein, advanced experimental characterization techniques, including in situ environmental transmission electron microscopy (eTEM) and CO 2 chemisorption by diffuse‐reflectance infrared Fourier transform spectroscopy (DRIFTS), transient 18 O‐isotopic exchange, and density functional theory (DFT), are employed to elucidate the mechanism of the CO 2 interaction with molten‐salt‐modified MgO in the 250–400 °C range. Herein, eTEM studies using low (2–3 mbar) and high (700 mbar) CO 2 pressures illustrate the dynamic evolution of the molten NaNO 3 salt promoted and unpromoted MgO carbonation with high magnification (<50 nm). The formation of 18 O‐NaNO 3 (use of 18 O 2 ) and C 16 O 18 O following CO 2 interaction, verifies the proposed reaction path: conversion of NO 3 − (NO 3 − → NO 2 + + O 2– ), adsorption of NO 2 + on MgO with significant weakening of CO 2 adsorption strength, and formation of [Mg 2+ … O 2− ] ion pairs preventing the development of an impermeable MgCO 3 shell, which largely increases the rate of bulk MgO carbonation.